Underground piping systems are essential for transporting liquids and gases to homes and businesses. Utilities typically use these piping systems for sewer, water, gas, and other applications. Such piping systems are installed several feet underground and access to the piping systems is therefore limited.
Underground pipes experience cyclical loadings, premature wear, corrosion, porosity, and ambient foundation or earth movements. These factors contribute to the overall deterioration of the pipes. Often the pipes develop damaged or weakened areas requiring repair.
To maintain the service afforded by the underground piping system, any cracks or leaks must be promptly detected and repaired. Such repair generally requires the replacement of a long length of the pipe, since the repair of a small section of the pipe by welding, patching or otherwise, is usually unsatisfactory and difficult or even impossible because the pipe diameter does not allow human access in safe conditions. In the case of an underground pipe, the replacement of the pipe is difficult, expensive, and time consuming.
A solution for the repair of underground pipes is to repair a pipe while it is still in place. In-situ pipe repair procedures have been developed. Some procedures include the insertion of a pliable reinforcement liner into the damaged pipe. The liner typically has an outer diameter which is substantially the same as the inner diameter of the damaged pipe. The liner is pressurized so that it presses firmly along the inner wall of the damaged pipe. The expanded liner is then cured to form a new, rigid lining or surface within the original pipe.
There are several types of reinforcement or reinforcing liners. Some liners are made from a polyester material. Other liners utilize fibers that are impregnated with a synthetic resin. Fibrous mats are alternatively used as the material for a liner. Some reinforcement liners include glass fibers for support and strength, since glass fibers have a high strength and stiffness, while still possessing good resistance to elongation.
Some liners are hardened or cured after they have been installed. These liners are referred to as “cured-in-place pipe (CIPP)” liners. The resin in a cured-in-place liner bonds or adheres to the glass or other reinforcement fibers after it is cured. Due to the bond between the resin and the fibers, the resin also becomes more resistant to stretching when axial or radial loads are applied to the cured liner. Thus, the cured resin is reinforced by fibers so long as the bond between the resin and glass fibers is not broken.
The liners are typically installed in environments that are continuously exposed to water and other corrosive materials. In particular, due to the presence of anaerobic bacteria in sewage water, sewer pipelines often contain hydrogen sulfide, the oxidation of which develops diluted sulfuric acid in the sewage water. The liners are also exposed to varying temperatures and flow conditions. Thus, the liners should be designed to withstand such environments.
The liner inserted inside a pipe should also have good flexibility to stretch and adjust itself to the host pipe diameter before cure, and must have good strength characteristics and adequate stiffness after cure to resist ground settlement or ground movement particularly if the host pipe has lost its required structural integrity.
Production methodologies for producing CIPP glass liners include a folding process and a winding process.
As shown in FIG. 1, in a conventional folding process 100, multiple layers of fabric 102 (e.g., woven roving mat fabrics) are folded together with an overlap of several centimeters per layer around a inner tubular film 104 (e.g., a styrene tight tubular film). The total glass pack is then wrapped in an outer film 106 (e.g., a joint welded outer film). The number of fabric layers 102 depends on the required wall thickness. After preparing the dry tube, impregnation with a resin is performed. This impregnation step is often assisted by vacuum. The impregnated liner is then shielded from daylight/UV light to prevent premature curing of the resin.
To install the liner (formed by the folding process 100) within a pipe (e.g., a sewer pipe), the liner is pulled into the pipe and inflated using air pressure. The air pressure within the liner acts to push the liner against the inner surface of the pipe being rehabilitated. The different impregnated fabric layers 102 slide over each other enabling the liner to expand matching the shape of the original pipe, resulting in a very close fit. Finally, the liner is cured, such as by ultraviolet (UV) light delivered by a series of UV lamps traveling through the pressurized liner.
In a conventional winding process 200, fabric rolls of a limited width are first impregnated with a resin/thickening agent mixture and rewound for maturation. After a defined maturation period, the pre-impregnated rolls are unwound and the associated fabrics 202 spirally wounded on a mandrel 204 covered in a plastic foil 206, as shown in FIG. 2. This winding operation continues until the required laminate thickness is achieved. The pre-impregnated fabrics are then covered by a thermoplastic outer film and protected against daylight/UV light during storage and transport.
To install the liner (formed by the winding process 200) within a pipe (e.g., a sewer pipe), the liner is pulled into the pipe and inflated using air pressure. The air pressure within the liner acts to push the liner against the inner surface of the pipe being rehabilitated. Expansion of the liner is mainly achieved by stretching of the fabrics 202. Finally, the liner is cured, such as by UV light delivered by a series of UV lamps traveling through the pressurized liner.